I believe its by chance depending on your clownfish. I had bought a true perc and an ocellaris one time thinking that they were the same type of clown, but they got along fine together. They didn't breed, but they followed each other, fought with each other, things that couples do.
Yea they should if there the only clowns in your tank it happend with my grade b picasso and now soon to b gone snowflake picasso but no worries as I have a pair of snowcassos and grade a picassos now still lookin for a pair of c quest onyx and thinkin about gettin another pair of snowflakes